uas: improve error handling

(1) Handle data pipe errors: When the data urb failed we
    didn't transfer anything, update scsi_cmnd accordingly.
(2) Cancel data transfers when we got back an error on the
    status pipe.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>